Wasted a lot of time going through the troubleshooting guides to find out that "Ekta" from 48.ie customer support clarified to say that for roaming outside the EU, their stance is "If it is working for you then it's great but if it is not working for you then we don't have any trouble shooting steps for it."
If I'd known that I could have prepared for that. But now I can't receive calls/SMS while abroad. So, if you have any 2 factor authentication requirements like banking or online account management you're blocked until returning to Ireland.
What was your problem with roaming in the US?
Could you not get any connection to a local network at all?
Yes, kept getting SIM not registered when trying Verizon,AT&T, T-mobile carriers.
Did you try the tips here?